The present invention refers generally to a plate heat exchanger, in particular a plate heat exchanger in the form of an evaporator, i.e. a plate heat exchanger designed for evaporation of a cooling agent in a cooling agent circuit for various applications, such as air conditioning, cooling systems, heat pump systems, etc.
The present invention refers especially to a plate heat exchanger, including a plate package, which includes a number of first heat exchanger plates and a number of second heat exchanger plates, which are permanently joined to each other and arranged beside each other in such a way that a first plate interspace is formed between each pair of adjacent first heat exchanger plates and second heat exchanger plates and a second plate interspace between each pair of adjacent second heat exchanger plates and first heat exchanger plates, wherein the first plate interspaces and the second plate interspaces are separated from each other and provided beside each other in an alternating order in the plate package, wherein substantially each heat exchanger plate has at least a first porthole and a second porthole, wherein the first portholes form a first inlet channel to the first plate interspaces and the second portholes form a first outlet channel from the first plate interspaces and wherein the plate package includes a separate space for each of said first plate interspaces, which space is closed to the second plate interspaces.
The cooling agent supplied to the inlet channel of such a plate heat exchanger for evaporation of the cooling agent is usually present both in a gaseous state and a liquid state. It is then difficult to provide an optimum distribution of the cooling agent to the different plate interspaces in the evaporator in such a way that an equal quantity of cooling agent is supplied and flows through each plate interspace. It is known that this problem of the distribution of the cooling agent at least partly can be solved by providing a throttling of the cooling agent at each plate interspace. In such a way a pressure drop of the cooling agent is obtained when it enters the respective plate interspace.
SE-C-502 984 discloses a plate heat exchanger of the kind initially defined having an inlet channel for a cooling agent. The inlet channel is through compression-moulding of the heat exchanger plates completely closed to the second plate interspaces for the fluid to be cooled and has a number of small openings extending to each of the first plate interspaces. These openings form throttlings, which provide a certain pressure drop of the cooling agent at the entrance into the respective plate interspace. The small openings may be designed as a hole through the sheet of each heat exchanger plate or as a thin channel provided through the compression-moulding.
U.S. Pat. No. 5,971,065 discloses a similar plate heat exchanger having a number of small openings between the inlet channel for the cooling agent and the respective plate interspace. The plate heat exchanger according to U.S. Pat. No. 5,971,065 differs from the solution proposed in the above-mentioned SE-C-502 984 in that a common space for the cooling agent has been created through the compression-moulding between the inlet channel and the respective plate interspace for the cooling agent. This common space extends through substantially the whole plate package in parallel to the inlet channel. A plurality of small openings extend between the inlet channel and the common space, and at least one small hole extends between the common space and each of the plate interspaces for the cooling agent.
EP-B-1 203 193 disclosed another plate heat exchanger including a package with heat exchanger plates, which together with sealing means defines first plate interspaces and second plate interspaces. The inlet channel is partly closed to the first plate interspaces by means of loose gaskets. The inlet channel communicates according to an embodiment disclosed with the first plate interspaces by means of small pipes extending through the respective gasket and forming a small opening for throttling of the cooling agent flow.
With the solutions proposed in these documents, it can be difficult to obtain a sufficient pressure drop for achieving an acceptable distribution of the cooling agent in the different first plate interspaces. In particular, a large pressure drop is required for cooling agents having a relatively high density in a gaseous state, for instance the cooling agent R410a. Another problem with the solutions proposed in these documents is that they can be difficult to apply to plate heat exchangers having small dimensions. In such small plate heat exchangers, there is not sufficient space around the inlet channel for the proposed solutions. In particular, the small channels provided through compression-moulding can tend to be clogged when the heat exchanger plates having a small mould depth of the thin channels are brazed to a plate package.